Instead of a flat-plate display device that is fabricated using a hard glass substrate, a sheet-like display device using a flexible substrate such as a plastic film (such a display device being also referred to as “sheet display”) is currently under development. Since the sheet display is light in weight, hard to be broken, and capable of being folded or bent into a curved surface, it is expected to be developed for new applications.
In a display unit of the display device, pixels arranged in a matrix are driven by pixel circuits that are formed by thin-film transistors. Each of the thin-film transistors includes a semiconductor film, a gate insulating film, and a gate electrode, and each of the pixel circuits is formed by a scanning signal line, a video signal line, and the like that are provided via an interlayer insulating layer.
However, bending the flexible substrate cracks the gate insulating film and the interlayer insulating film, each of which is made of an inorganic insulating material over substantially the entire surface of the display unit, thus undesirably affecting the reliability of the display device. To address such a problem, Japanese Unexamined Patent Application Publication No. 2007-288078 discloses a structure in which, by removing those portions of a laminate of insulating films (i.e. a laminate including a gate insulating film and an interlayer insulating film) which are present in regions where no thin-film transistors are formed, this insulating film laminate is separated into islands.
Incidentally, a resin substrate that is used as the flexible substrate is higher in moisture permeability and moisture absorbency than a glass substrate and, as such, requires a barrier film constituted by a silicon nitride film or the like. In the display device disclosed in Japanese Unexamined Patent Application Publication No. 2007-288078, even those portions of the insulating films which are provided on foundation surfaces of the thin-film transistors are removed, with the result that moisture diffuses into the display device. Having diffused into the display device, the moisture causes deterioration not only in the thin-film transistors but also in display elements that are formed using liquid crystals and an organic electroluminescence material. Therefore, the display device disclosed in Japanese Unexamined Patent Application Publication No. 2007-288078 can be made higher in resistance to the bending of the flexible substrate but becomes lower in reliability due to the deterioration in the display elements caused by the moisture or the like.